Helical coordination polymers and cyclic dimers formed from heteroleptic thioether-dipyrrinato copper(II) complexes

Heteroleptic copper complexes containing an acetylacetonato ligand and a thioether derivatized dipyrrinato ligand are shown to form oligomers and polymers in the solid state.     

Preconcentration and speciation of chromium using a melamine based polymeric sequestering succinic acid resin: its application for Cr(VI) and Cr(III) determination in wastewater

A new melamine based polymeric sequestering resin was prepared for preconcentration and separation of hexavalent chromium from water, and its sequestering action was investigated. The water-insoluble, cross-linked sequestering resin was formed by reaction with bromosuccinic acid and cross-linking of melamine. The active sequestering group on the resin is NH-(Succinic acid) or salt thereof. The resulting chelating resin was characterized by infrared spectra. The newly prepared resin quantitatively retained Cr(VI) at pH 2.0-4.0 when the flow rate was maintained between 1 and 5 ml min⁻¹. The retained Cr(VI) was instantaneously eluted with 25 ml of 0.1 M NaOH. The chromium species were determined by a flame atomic absorption spectrometer. The limits of detection for Cr(VI) and Cr(III) were found to be 5.3 and 4.2 μg l⁻¹, respectively. The precision and accuracy of the proposed procedure was checked by the use synthetic and reference steel samples. The established preconcentration method was successfully applied to the determination and selective separation of Cr(VI) in electroplating industry wastewater. Total concentrations determined by the spectrophotometric method (110.3±0.6 g l⁻¹ Cr(VI) and 1.2±0.3 g l⁻¹ Cr(III)) are compared with those found by FAAS and the obtained results (110.4±1.8 g l⁻¹ Cr(VI) and 1.4±0.5 g l⁻¹ Cr(III)) show good agreement.     

Speciation analysis of chromium by separation on a 5-palmitoyl oxine-functionalized XAD-2 resin and spectrophotometric determination with diphenylcarbazide

The method developed in this work for the separation and preconcentration of Cr(III) is based on its retention by an Amberlite XAD-2 copolymer resin functionalized with 5-palmitoyl-8-hydroxyquinoline (oxine), abbreviated XAD-POx, with the ligand covalently bound to the copolymer. Cr(III) sorption was quantitative within the pH range 4.5–7.0 and Cr(VI) was not retained. The Cr(III) held by the resin column was eluted with a hot solution of H₂O₂ in pH9.0 aqueous NH₃–NH₄Cl buffer, and Cr oxidized to CrO₄^2– was rejected by the chelating cation-exchanger column. Any Cr(VI) originally present with Cr(III) could be reduced with an acidic solution of H₂O₂, and retained by the column yielding total Cr results, Cr(VI) being determined from the difference. The resin showed a maximal preconcentration factor of 60 for Cr(III), the LOD and LOQ being 9.3 and 30.1 nmol L^–1, respectively. The developed preconcentration-speciation analysis was finished with a diphenylcarbazide (DPC) spectrophotometric procedure suitable for conventional laboratories. The resin showed excellent salt tolerance, enabling Cr analysis in seawater, and was stable over extended use. All the interferents of this procedure that normally occur in an electroplating effluent, a blended coal CRM, and a standard steel sample could be removed by the recommended procedure, by use of partial and total selectivity at the adsorption and desorption stages, respectively, enabling preconcentration and colorimetric determination of chromium in various complex matrices.     

The p38 mitogen-activated protein kinase is involved in stress-induced phospholipase D activation in vascular smooth muscle cells

Oxidative stress has been implicated in mediation of vascular disorders. Earlier study showed that the exposure of vascular smooth muscle cells (VSMC) to pervanadate (hydrogen peroxide plus orthovanadate) resulted in the accumulation of [3H]phosphatidylbutanol. In this study, the effect of pervanadate on the activation of p38 mitogen-activated protein kinase (p38 MAPK) was studied in the VSMC. Pervanadate treatment activated p38 MAPK in a dose-and time-dependent manner. Interestingly, specific inhibition of p38 MAPK with SB203580 attenuated pervanadate-induced PLD activation. This correlates with the finding that expression of dominant negative mutants of MKK3/6 inhibited the PLD activation. SB203580 pretreatment also inhibited other cellular stressors (i.e. high osmolarity and UV light)-induced PLD activation. The possible correlationship of p38 MAPK activation with PKC was examined since PKC is reported to be involved in the pervanadate-induced PLD activation. Calphostin C, a PKC inhibitor, suppressed pervanadate-induced p38 MAPK and PLD activation in a dose-dependent manner. These results suggest that PKC-p38 MAPK may represent an upstream pathway of PLD in the signal transduction of cellular stress.     

Notable coordination effects of 2-pyridinesulfonamides leading to efficient aziridination and selective aziridine ring opening

[reaction: see text] We have developed, on the basis of a chelation-strategy, an efficient copper-catalyzed aziridination protocol with the use of 5-methyl-2-pyridinesulfonamide and PhI(OAc)(2). The reaction proceeds smoothly under mild conditions to give aziridines in moderate to good yields in the absence of external ligands or bases. The coordination-assisted approach offers the additional benefits that efficient deprotection of the N-substituent and selective aziridine ring-opening are effectively achieved.     

The effect of solvent composition on swelling and shrinking properties of poly(acrylamide-co-itaconic acid) hydrogels

The peculiarities of the equilibrium swelling ratio and swelling-shrinking kinetics of polyelectrolyte copolymeric hydrogels consisting of acrylamide and itaconic acid (AAm/IA) have been studied in water/nonsolvent (acetone, methanol, ethanol and 1-butanol) mixtures as a function of solvent composition and IA content in the hydrogel. The phase transition of these hydrogels was generated by changing the solvent composition by progressive substitution of water by the nonsolvent. For all P(AAm/IA) hydrogels, the form of the shrinking curves was determined to be strongly dependent on the type of the nonsolvent used. The rate of shrinking of these hydrogels increased in the order 1-butanol < ethanol < methanol < acetone.     

New tetradentate Schiff-base polymers: preparation of poly[2,5-(didodecyloxy)phenylene-1,4-diyl-alt-N,N-(o-phenylene)-bis(salicylideneiminato-4,4-diyl)] and poly[2,5-(didodecyloxy)phenylene-1,4-diyl-alt-N,N-(alkylidene)-bis(salicylideneiminato-4,4-diyl)]s

New tetradentate Schiff-base polymers, in which phenylene units alternate with salicylideneiminato units, have been prepared by condensation of 2,5-(didodecyloxy)-1,4-bis(3-formyl-4-hydroxyphenyl)benzene (DFHB) with appropriate diamines in a mixed solution of CHCl₃/toluene/acetic acid with 31-79% yields. DFHB as the key building block was prepared by the Suzuki reaction of 2,5-(didodecyloxy)benzene-1,4-diboronic acid with 5-bromosalicylaldehyde in a two-phase solution of tetrahydrofuran/water in the presence of NaHCO₃/Pd(PPh₃)₄ in 45% yield. The molecular structures of the prepared compounds were identified by spectroscopy. Their absorption spectroscopic profiles have been analyzed.     

FT–IR spectroscopic study on the thermal and thermal oxidative degradation of nylons

The effects of heat and oxygen on nylon films were studied by FT–IR spectroscopy. Nylons 6, 66 and nylons containing carbonyl groups in either the diamine or the diacid moiety were prepared. Nylon films cast on aluminum were studied in an environmental chamber under controlled conditions. The progress of chemical and physical changes was monitored by FT–IR spectroscopy. Thermal energy caused largely an increase in crystallinity due to annealing and also an increase of nonhydrogen-bonded amide groups, which seemed to entail mainly amide groups from the amorphous region. The intensities of IR absorption bands related to the folded structure reduced as soon as heating began. The IR spectra of the carbonyl groups formed by thermal oxidation showed band shapes that indicated that the formed carbonyl groups were of many different origins. The presence of keto groups purposely inserted into the backbone chains increased the rate of oxidation. Pyrolysis of the nylons was also studied to supplement data obtained at lower temperatures.     

Synthesis of the C3-C19 segment of phorboxazole B

[reaction: see text]. Three segment-coupling Prins approaches to the C3-C19 segment of phorboxazole B have been developed. One successful strategy utilized a novel TMSBr-mediated cyclization that proceeded with complete axial selectivity. Displacement of bromide with cesium acetate provided the C13 hydroxyl stereocenter of 22. Additionally, treatment of alpha-acetoxy ether 20 with TFA enabled a more concise synthesis of the C3-C19 target 13 by allowing direct access to the equatorial alcohol.     

Effect of surface-perturbed intermolecular interaction on adsorption of simple gases on a graphitized carbon surface

In this paper, we investigate the effect of the solid surface on the fluid-fluid intermolecular potential energy. This modified fluid-fluid interaction energy due to the inducement of a solid surface is used in the grand canonical Monte Carlo (GCMC) simulation of various noble gases, nitrogen, and methane on graphitized thermal carbon black. This effect is such that the effective interaction potential energy between two particles close to surface is less than the potential energy if the solid substrate is not present. With this modification the GCMC simulation results agree extremely well with the experimental data over a wide range of pressures while the simulation results with the unmodified potential energy give rise to a shoulder near the neighborhood of monolayer coverage and the significant overprediction of the second and higher layer coverages. In particular the unmodified GCMC results exhibit very sharp change in those higher layers while the experimental data have a much gradual change in the uptake. We will illustrate this theory with adsorption data of argon, xenon, neon, nitrogen, and methane on graphitized thermal carbon black.